Gas analysis method

ABSTRACT

A method and apparatus for continuously measuring the proportion of one gas in a mixture of gases by selectively removing the one gas and thereafter measuring the partial pressure change in one or more of the remaining constituent gases brought about by removal of the one gas and thereby determining the proportion of the one gas in the original mixture.

United States Patent Inventor Philip Reichner [56] References Cited A I N 5 2 332 UNITED STATES PATENTS P 2,036,251 4/1936 Boynton 4. 23/232 F11ed Nov. 12, 1968 3,301,775 1/1967 Tslen 204/195 Paemed 1971 3 334 513 8/1967 Thomas 73/23 Assgnee ga g' g ii 3,408,269 10/1968 Hersch .1 204 195 3,514,377 5/1970 Spacil et a1. .4 204/195 Primary Examiner-T. Tung Attorneys-F. Shapoe and Lee P. Johns GAS ANALYSIS METHOD 7 Claims 12 Drawing Figs ABSTRACT: A method and apparatus for continuously mea- U.S. C1 204/1 T, suring the proportion of one gas in a mixture of gases by el 204/195 tively removing the one gas and thereafter measuring the par- Int.Cl ..G0ln 27/46 tial pressure change in one or more of the remaining con- Field of Search ..23/232, 232 istituent gases brought about by removal of the one gas and E, 254, 254 E, 255, 255 E, 256; 73/23; 204/1.l, thereby determining the proportion of the one gas in the 195 original mixture.

SCRUBBER IO 1 l8 l6 SE N SOR I? I PATENTEDuov 1s l97l 3, 520 9 3 SHEET, 1 [IF 2 FIG.|. l2

SCRUBBER l6 SENSOR 5 FIG.2.

SCRUBBER DRYER 16 I8 SENSOR I0 I J SCRUBBER DRYER SENSOR DRYER -24 FIG.4

' SCRUBBER IO J SENSORS l9 l2 F|G 9 SCRUBBER DRYER I6 SENSOR 60* J DRYER I4 \24 I5 SOURCE OF KNOWN GAS SCRUBBER DRYER FIG. I0. I

C22 sENsoR IO I4) 50.

3 DRYER h PATENIEDunv 1s l97| SHEET 2 [IF 2 I Ga IIIIILJIIIITII FIG.5.

EXHAUST 0 L M UV/ W L 5 Ki? l |v I new) m h L 1 H 2 I! H M 50 1/ I 1 VA/ r A. "II A H I H 3 M m I 8 IF 1 2 U 4 m 6 M 0 M "m UUM mmm w m a w L, iii, Cr Z I+ A T 1 O2 E U ,3 4 MM mmmmmmmmm% l H x US P w/ 4/ RM 8 /h 4 T' l \!4 1 1 III: I) 1 w I U I W 1 EL n U m 1 1 wa I SA G F|G.l2.

- 0 GAUGE o MASS SPEC 2O 40 LAB MIXTURES,% (PRESSURE BASIS FIG. ll.

. 0 GAUGE o MASS SPEC SUPPLlER ANALYSIS, CO2

SUPPLIER ANALYSIS, CO2

GAS ANALYSIS METHOD BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a gas analysis method and device. More particularly, it pertains to apparatus for continuously and quantitatively measuring the proportion of one gas in a mixture of gases.

2. Description of the Prior Art Various techniques and apparatus for using such techniques have been known for making quantitative gas analyses. These techniques have been generally based on the properties of the gas to be measured. Instruments for specific analysis have been employed such as oxygen or carbon dioxide analyzers. A disadvantage of such instruments is their inordinate cost which is additive when more than one gas is measured.

Associated with the foregoing is the fact that analyzers, particularly for medical purposes, should be capable of giving results in a relatively short time. Moreover, analyzers such as continuous oxygen or carbon dioxide analyzers must be stable, reliable, and accurate. In addition, prior devices that continuously measure change in a gas mixture have been limited to samples of relatively constant compositions.

SUMMARY OF THE INVENTION It has been found in accordance with this invention that the foregoing disadvantages may be overcome and the indicated requirements met by the apparatus disclosed herein which, among other things, provides for continuously measuring the amount of a constituent gas in a mixture of gases and includes means for continuously sampling an initial gas mixture containing a constituent gas to be analyzed, by dividing it into two streams of means for selectively removing the constituent gas from the initial mixture in one of the streams to form a second mixture, means for measuring the partial pressure of a second component of the initial mixture and of the second mixture in the streams, and means for comparing the partial pressures of the second component gas in both streams and relating the difference to the quantity of the constituent gas in the initial mixture.

Accordingly, it is an object of this invention to provide a gas analysis apparatus for analyzing a continuous sample of a gas mixture for a constituent part thereof.

It is another object of this invention to provide a gas analysis apparatus which is stable, reliable, and accurate over a large range of measurement.

Finally, it is an object of this invention to satisfy the foregoing objects and desiderata in a simple, effective, and economical manner.

Generally, the gas analysis device of the present invention comprises at least two conduits for introducing separate streams of a selected gas mixture to be analyzed, for a given component, removal of the given gas component to be measured in at least one of the conduits to provide a second mixture therein, both gas streams having another gas component and at least one electrolytic cell including at least two separate chambers into which the streams from the conduits are separately introduced, whereby the partial pressures of the said other gas component to be measured in the initial gas mixture and in the second mixture are compared and related to the proportion of the given gas component to be measured in the original gas mixture.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the nature and objects of this invention, reference is made to the drawings in which similar numerals refer to similar parts throughout the several views of the drawings, and in which:

FIGS. 1 to 4, 9, and are schematic views of several embodiments of the invention:

FIG. 5 is a longitudinal sectional view of an electrolytic cell for measuring oxygen partial pressures;

FIG. 6 is a transverse sectional view taken on the line V-V of FIG. 5;

FIG. 7 is a longitudinal sectional view of a dual-cell arrangement for simultaneous measurement of two gas components, such as oxygen and carbon dioxide, for medical respiratory quotient measurements, or carbon dioxide and water vapor for industrial gas measurements;

FIG. 8 is a transverse sectional view of the line VllI-VIII of FIG. 7;

FIG. 11 is a graph showing the accuracy of CO, measurement by an 0, cell as compared with measurements by mass spectrometry in the O to 5 percent C0, rough; and

FIG. 12 is a graph similar to that of FIG. II in the 0 to percent C0, range.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown schematically in FIGS. 1, 2, 3, and 4, various embodiments of the device of the invention may be employed. In the drawings, the device includes an inlet conduit 10 for conveying a sample of the gas mixture to be analyzed which is divided into two branch conduits I2 and 14. The conduit 12 includes a gas removal member 16 which may be a scrubber or other means for removing the gas component to be measured. Both conduits l2 and 14 are connected to a sensor 18 to be described in detail subsequently. As shown in FIG. 2 a dryer 20 is provided in the conduit 10. In FIG. 3, a dryer 22 is provided in the conduit 12 downstream from the scrubber I6, and a dryer 24 is provided in the conduit 14.

The several embodiments of the invention as shown in FIGS. 1, 2, 3, and 4 are provided with a single inlet conduit I0 by which the sample gas stream is introduced into the device. However, the single inlet conduit 10 (FIGS. 1, 3, and 4) may be deleted, and the gas to be analyzed drawn directly into the conduits 12 and 14, provided such conduits are sufiiciently close together to obtain representative gas samples of similar composition. FIG. 4 shows an embodiment in which two specific gas sensors 19, such as polarographic cells are utilized.

As was indicated above, the purpose of this device is to continuously and quantitatively measure the proportion of one gas in a mixture of gases by the selective removal of the one gas and subsequently measuring the resulting change in the partial pressure of one or more of the remaining components. One technique for the removal of the gas to be measured is by scrubbing" the specific gas from the original mixture, such as by chemical combination, adsorption, electro chemical reaction, and chemical hydration. The scrubber 16, for example a container with a suitable compound for chemically or physi cally extracting a desired gas component, is disposed in the conduit 12. Where carbon dioxide (C0,) is to be measured in a mixture of other gases such as air, the scrubber I6 is filled with a suitable material for adsorbing carbon dioxide such as lithium hydroxide or sodium hydroxide either as pellets, sticks, or concentrated aqueous solution thereof. The water vapor generated by this reaction may be removed by employing an absorbent material for water at the outlet of the scrubber. As an alternative, a particular molecular sieve may be used to selectively remove water vapor, carbon dioxide, or other gas. If oxygen is to be removed, an oxygen cell may be used to electrochemically pump the oxygen out of the system.

In a similar manner, it may be desirable for some purposes to remove water vapor from the gas sample if its presence otherwise alfects the results of the sensor. For that purpose a single dryer 20 (FIG. 2) is provided in the inlet conduit 10 or, in the alternative, separate dryers 22 and 24 are provided in the branch conduits l2 and 14, respectively (FIG. 3). The dryers 20, 22, and 24 are filled with a suitable water absorbent material such as anhydrous calcium sulfate. Other means for removing water include molecular sieve (adsorption), and chemical hydration.

The device may be operated without the use of water vapor absorbent as shown in FIG. 1 if no water is generated in the scrubber or if the sample is fully water saturated. For a sample gas with a high water content, a water dryer 20 is placed in the inlet conduit 10, as shown in FIG. 2, where it is conveniently replaced when exhausted.

The sensor 18 may include any type of electrolytic cell by which an efiective ratio or difference of the partial pressures of a constituent gas contained in both gas streams entering the sensor through the conduits l2 and 14, may be measured. One type of such a sensor is that shown in FIGS. 5 and 6 which includes an electrolytic cell 26, a casing 28, insulation 30,'and a heater 32. The cell 26 includes two half portions 34 and 36 as shown in FIG. 5. The half portions 34 and 36 are disposed on opposite sides of a solid electrolyte 38 on the opposite sides of which are mounted electrodes 40 and 42.

As assembled the cell half portions 34 and 36 together with the electrolyte 38 provide separate chambers 44 and 46 in which the electrodes 40 and 42, respectively, are disposed. The upper ends of the chambers 44 and 46 communicate with separate conduits 48 and 50 which in turn communicate respectively with the conduit portions 12 and 14. The electrodes 40 and 42 are provided with corresponding lead wires (not shown) which are connected to a readout (not shown) in a conventional manner.

For a zirconia electrolyte oxygen cell the heater 32 may be operated as low as 600 C. but is preferably operated at a temperature above 825 C. However, for other types of cells the operating temperature may be as low as the ambient temperature of the sensor.

When making carbon dioxide measurements a continuous sample of gas is split into two paths, one containing a dryer and the other containing a dryer and C0 adsorbent as in FIG. 3. The dry gases in the second path are greater in volume percent by the ratio l/l-C, where C is the volume fraction of C0 absorbedv If the total pressures on the two sides of the cell are maintained constant (or at a constant ratio), then the two paths fed into the sensor result in a cell voltage displacement of:

AE=K log l-C), and and therefore C=l-antilog (AE/K).

The cell voltage is related only to the scrubbed gas amount and is independent of the quantity of gas for which the cell is nonnally specific.

The technique herein disclosed can be used to measure any gas component that can be selectively scrubbed.

A modified form of cell is shown in FIGS. 7, 8, 9, and which-is applicable to continuous simultaneous monitoring of carbon dioxide evolution rate andthe rate of oxygen consumption in human respiration. By evaluating the ratio of these two rates, a person's respiratory quotient is obtained. For that purpose an integrated dual-cell sensor 60 (FIGS. 7 and 8) is provided with three conduits l2, l4, and 15. As

shown in FIG. 9 the conduit delivers a stream of gas mixture containing a known proportion of oxygen, the conduit 14 delivers a stream of air having oxygen depleted by respiration and water vapor removed by the dryer 24, and the conduit 12 delivers a stream of the same air having CO removed by the scrubber l6 and water vapor removed by the dryer 22.

The sensor 60 (FIGS. 7 and 8) is similar to that shown in FIG. 5 in that it includes a casing 28, insulation 30, a heater 32, and two half portions 34 and 36 having conduits 48, 50, and 51 connected to the conduits l2, l4, and 15, respectively. In addition, the sensor, being an electrolytic cell, includes a pair of solid electrolytes 52 and 54 which are spaced from each other by a U-shaped spacer 56 (FIGS. 7 and 8), and which form a chamber 58 into which the conduit 50 delivers a sample of dried gas. Manifestly, the air that is devoid of CO and H, is carried to the reaction chamber 44 on the side of the electrolyte 52 opposite the chamber 58. A resulting cell voltage which is related to the carbon dioxide content of the respiration gas mixture, is transmitted by the metal electrodes 62 and 64 on reverse sides of the electrolyte 52 and carried by lead wires (not shown) to a readout or to computational circuitry in a conventional manner. Similarly, a gas mixture containing a known proportion of oxygen is delivered to the reaction chamber 46 on the side of the electrolyte 54 opposite the chamber 58, and a resulting cell voltage which is related to the oxygen content of the respiration gas mixture, is transmitted by the metal electrodes 66 and 68 on the reverse sides of the electrolyte 54 and carried to a readout or to computational circuitry. Thus, the dual-cell sensor 60 can be used to simultaneously monitor oxygen consumption and CO, evolution and to thereby obtain a respiratory quotient.

In a similar manner any gas mixture may be analyzed for two gas components that can be selectively scrubbed. For example, in FIG. 10 the sensor 60 may be used to analyze an unknown gas mixture for two components such as water vapor and C0 The unknown gas mixture may be introduced at conduit 10 through the conduits l2, l4, and 15 to the sensor 60. As shown in FIG. 10, the conduit 15 delivers a stream of unmodified gas mixture, the conduit 14 delivers a stream of the same gas mixture having water vapor removed by the dryer 24, and the conduit 12 delivers a stream of the same gas mixture having CO removed by the scrubber l6 and water vapor removed by the dryer 22. In the manner described above, a resulting cell voltage which is related to the carbon dioxide content of the original gas mixture is transmitted by the metal electrodes 62 and 64 (FIG. 7) on the reverse sides of the electrolyte 52, and carried by lead wires (not shown) to a readout in a conventional manner. Similarly, a resulting cell voltage which is related to the water vapor content of the original gas mixture, is transmitted by the metal electrodes 66 and 68 on the reverse sides of the electrolyte '54, and carried by lead wires to a second readout in a conventional manner.

As an indication of sensitivity, ambient room air has been analyzed for its content of carbon dioxide (about 0.05 percent). For that purpose the air is drawn into the device through an inlet conduit 10 (FIG. 3) as an initial gas mixture containing among other things carbon dioxide, oxygen, and nitrogen. A portion of the original mixture is flowed into the scrubber 16 which contains an adsorbent of carbon dioxide such as lithium hydroxide granules. As a result of the reaction of carbon dioxide with lithium hydroxide, moisture is produced which is subsequently absorbed in the vapor removal housing 22 which is filled with granules of a desiccant such as anhydrous calcium sulfate. (A larger mesh size with indicator provides a faster response because of the lower surface area for adsorption of CO Thereafter the resulting mixture enters the sensor I8 via the conduit portion [2 as a second mixture devoid of carbon dioxide and moisture. At the same time another portion of the initial gas mixture passes through the water vapor removal housing 24 also containing a desiccant and enters the other side of the sensor via the branch conduit portion 14. When the two modified mixtures of gas enter the cell chambers 44 and 46 separately (FIG. 5), the cell 26 provides an electrical output, AE=K log p,/ p where p, and p, are the partial pressures of oxygen on opposite sides .of the electrolyte, which as shown above is expressed as AE=K log (l--'" C), where 'C is the room air volume fraction of carbon dioxide. For measurements in this range (""c=0to 0.0l log (l'" 'C) is closely equal to 'C/ ln l0, and E=K"'"C, a linear readout.

The following example is exemplary of the invention: EX- AMPLE Accuracy measurements were made over the range of 0.5 to percent CO Measurements in the range of 0.5 to 4 percent were obtained for bottled gases with supplier analyses available. Gases in the range of i0 to 90 percent were mixed in the lab (CO and air) on a partial pressure basis. Mass spectrometer analyses were used to check a number of these samples. The Table presents a summary of the carbon dioxide measurements.

The mass spectrometer measurements were consistently higher than the Suppliers analyses by 0.04 to 0.07 percent C0,. The mass spectrometer measurement for the 3.22 percent CO sample was not shown because the deviation was relatively large (2.97 percent CO reading) and an error was TABLE.-SUMMARY OF MEASUREMENTS [Concentration of CO (volume percent)] Sample Supplier Pressure Mass spec- Oz Number analysis basis trometer analyzer Variance probable either in preparation of the sample or in the analysis.

ratio of their partial pressures was equal to the desired ratio of volume percentages. The total cylinder pressure after mixing was about 100 p.s.i. The resulting measurements are shown in FIGS. 11 and 12. Errors in the mixing by this technique were predicted to be greater than the variance of the measured values shown in the Table. For the two sample mixtures l0 and 60 percent) that were checked by mass spectrometer measurements, the deviations of the oxygen analyzer measurement from the mass spectrometer readings were 0.03 and 0.19 volume percent C0,, or 0.3 percent error. This supports the conclusion that the deviations shown in FIG." are due to mixing errors rather than measurement errors.

Accordingly, the device of this invention enables measurement of any specific gas, use of a conversion unit by which the monitoring of one gas is the basis for measurement of another gas, and use of multiple-gas measuring cells that permit continuous simultaneous measurement of more than one component of a gas sample. The device performs with adequate stability and accuracy for monitoring of respiratory quotient in medical applications, and has been shown to be accurate over the range of 0.5 to 90 percent of carbon dioxide.

It is understood that the specification and drawings are merely exemplary and not in limitation of the invention.

What is claimed is:

l. A method for continuously measuring the proportion of a first constituent gas in a mixture of gases comprising continuously providing two sample streams of an initial gas mixture, selectively removing the first constituent gas from the initial gas mixture in one of the streams to form a second mixture, passing the stream representing the initial mixture in contact with a surface of a solid electrolyte member, passing the stream representing the second mixture in contact with the opposite surface of said solid electrolyte member, measuring the partial pressures of a second constituent gas in the initial mixture and in the second mixture, comparing these pressures and relating the difference to the proportion of the first constituent gas in the initial mixture.

2. The method of claim I, wherein the ratio of the total pressures of the initial mixture and of the second mixture is substantially constant.

3. The method of claim 1 wherein the total pressures of the initial and second mixtures are equal.

4. The method of claim 1 wherein the first constituent gas is C0 5. The method of claim 1 wherein said second constituent gas is oxygen.

6. A method for continuously measuring the proportion of two constituent gases in a mixture of gases comprising continuously providing three sample streams of an initial gas mixture, selectively removing one of said constituent gases from the initial gas mixture in one of the sample streams to form a second mixture, selectively removing both of said constituent gases from the initial gas mixture in another of the sample streams to form a third mixture; passing the stream representing the initial mixture in contact with a surface of a first solid electrolyte member, passing the stream representing the second mixture in contact with the opposite surface of said first solid electrolyte member and a surface of a second solid electrolyte member, passing the stream representing the third mixture in contact with the opposite surface of said second solid electrolyte member, measuring the partial pressures of a third constituent gas in the three mixtures, comparing the par- 

2. The method of claim 1, wherein the ratio of the total pressures of the initial mixture and of the second mixture is substantially constant.
 3. The method of claim 1 wherein the total pressures of the initial and second mixtures are equal.
 4. The method of claim 1 wherein the first constituent gas is CO2.
 5. The method of claim 1 wherein said second constituent gas is oxygen.
 6. A method for continuously measuring the proportion of two constituent gases in a mixture of gases comprising continuously providing three sample streams of an initial gas mixture, selectively removing one of said constituent gases from the initial gas mixture in one of the sample streams to form a second mixture, selectively removing both of said constituent gases from the initial gas mixture in another of the sample streams to form a third mixture; passing the stream representing the initial mixture in contact with a surface of a first solid electrolyte member, passing the stream representing the second mixture in contact with the opposite surface of said first solid electrolyte member and a surface of a second solid electrolyte member, passing the stream representing the third mixture in contact with the opposite surface of said second solid electrolyte member, measuring the partial pressures of a third constituent gas in the three mixtures, comparing the partial pressures and relating the differences to the quantity of the said two constituent gases in the initial mixture.
 7. The method of claim 6 wherein the partial pressure differences between initial, second, and third mixtures are denoted as voltages. 